GMATPrep Average

[eyelikecheese]

A certain car averages 25 miles per gallon when driven in the city and 40 miles per gallon when driven on the highway.According to these rates, which is the following average number of milers per gallon that the car travels when it travels 10 miles in the city and 50 miles on the highway?

A.)28
B.)30
C.)33
D.)36
E.)38



This is a very simple problem, but I keep coming up with 37.5 as the average?

The OA is 38

[Rahul@gurome]

Total miles = 10 + 50 = 60 miles
When driven in the city, gallons = 10/25 = 2/5 = 0.4
When driven on the highway, gallons = 50/40 = 5/4 = 1.25
Total gallons = 0.4 + 1.25 = 1.65
Therefore, average number of miles per gallon that the car travels = 60 miles/1.65 gallons = 36.36 miles per gallon

[spoiler]The correct answer is D.[/spoiler]

Can you check the OA please?

[eyelikecheese]

Sorry the OA is 36 indeed. I was doing a weighted average of 25(10)+50(40)/60 which gave me 38. I see the correct method now. Thanks!

[Rahul@gurome]

Sorry the OA is 36 indeed. I was doing a weighted average of 25(10)+50(40)/60 which gave me 38. I see the correct method now. Thanks!

welcome

[Everest]

A certain car averages 25 miles per gallon when driven in the city and 40 miles per gallon when driven on the highway.According to these rates, which is the following average number of milers per gallon that the car travels when it travels 10 miles in the city and 50 miles on the highway?


In city, 10 miles can be drove with .4 Gallons

In Hgwy, 50 miles cab be drove with 1.25 Gallons

=> 60 miles are be drove by 1.65 Gallons.
so, average number of miles per gallon that the car travel is 60/1.65 = 36.36


IMO is D

D.)36